The present invention relates to a mechanical fastener and more particularly to a mechanical fastener used to secure a tube and a linkage of a linkage assembly such as those found in automobile seat assemblies.
A wide variety of conventional mechanical fasteners are known, including fasteners used to secure tubular members. For example, mechanical fasteners are used in automobile seat assemblies to axially and rotationally secure a tubular member to a linkage. The linkage may then be secured to a support which provides the mounting for the seat assembly. It is also known to weld such tubes to a linkage for use in an automobile seat assembly.
One such known fastener which can be used to secure a tube to a linkage in an automotive seat assembly comprises an insert having a main body portion with a hexagonal cross section. One end of the hexagonal insert may be tapered with the diameter of the inserted end being smaller than the hexagonally shaped main body portion. After the tube is positioned within an opening in the linkage, the tapered end of the insert is forced into the open end of the tube. The tube is deformed outwardly by the insert to engage the linkage and thereby secure the tube within the opening in the linkage.
When using a hexagonal shaped insert, the tube will oftentimes not completely conform to the shape of the hex insert. Instead the tube will engage the insert at the intersection of the flats of the hexagonal portion of the insert leaving spaces between the flats of the insert and the inner diameter of the tube. Since the tube and insert are not engaged at those locations where the tube is spaced from the insert, the surface area of the tube and insert at such spaced apart locations does not directly contribute to the frictional forces retaining the insert within the tube.
Another characteristic of such hexagonally shaped inserts is that such inserts oftentimes have a relatively sharp transition between the tapered portion at the end of the insert and the intersections of the flats of the insert which are present in the hexagonal shaped main body portion of the insert. The geometry of the insert creates stress concentrations in the tube which, if they become too great, can cause the tube to split.
It is desired to provide an improved mechanical fastener which provides a strong connection between a tube and a linkage and limits the potential for splitting the tube during assembly.